As part of the Reporting API, Deprecation Reports can be enabled with a single line of code or config on your website.
If your site is using a feature that a browser will soon deprecate, you will receive a report to warn you when that feature will stop working.
If browsers are sending deprecation reports, then it means that you have a feature on your website that will be affected.
These reports are low volume and hopefully you never receive any, meaning no cost, but if you do, they need your attention
Alongside deploying DMARC, you may like to further improve the security of your emails.